1. Field of the Invention
The invention generally relates to mobile robots. In particular, the invention relates to a relatively economical and efficient technique to permit a mobile robot to detect a motional state.
2. Description of the Related Art
Mobile robots are becoming more and more commonplace in society. It will be understood that these robots can be embodied in various forms, such as in automated vacuum cleaners. A variety of applications can be found for mobile robots, such as, but not limited to, entertainment applications, such as toy robots, utility applications in environments that are unfriendly to humans, such as space, deep water, cold temperature, radiation, chemical exposure, biohazards, etc., dangerous tasks such as defusing of potential explosives, operation in confined spaces, such as collapsed buildings, the performance of menial tasks, such as cleaning, etc.
In many of these applications, relatively autonomous behavior from the mobile robot is desirable without an excessive amount of human interaction. One ability that significantly enhances the ability for a mobile robot to operate autonomously is the ability to move safely.
Conventional techniques for obstacle avoidance include the use of proximity sensors. For example, the TRILOBITE®, a mobile robot embodied as an automated vacuum cleaner available from Electrolux AB of Sweden, uses sonar sensors to detect obstacles in the vicinity of the robot. As another example, the RoboScout Personal Robot, available from Sharper Image Corporation, employs infrared sensors for a similar purpose. Even more sophisticated obstacle detection systems can be found in industrial applications. For example, the Pioneer series of robots from ActivMedia Robotics, LLC, uses a laser range finder to detect nearby obstacles. Disadvantageously however, proximity sensors often do not reliably detect obstacles and can be relatively expensive. For examples, proximity sensors can suffer from blind spots and can often fail to reliably detect obstructions. For example, a laser range finder typically performs proximity detection in a single plane such that an obstacle of non-uniform shape, such as an obstacle with a bump or an overhang, may not be reliably detected as an obstacle by the laser range finder.
Other mechanisms can also permit a mobile robot to move about safely. For example, the Roomba™, which is a mobile robot embodied as an automated vacuum cleaner available from iRobot Corporation, uses a contact sensor to detect a collision between the robot and an obstacle. Contact sensors are also known in the art as “bump sensors.” In response to the detection of the collision, the robot can subsequently adjust the robot's path. Disadvantageously however, contact sensors may not reliably detect collisions between the robot and an obstacle. For example, a bump sensor typically provides coverage for only a relatively small portion of the robot's surface area; thus, an obstacle that contacts the robot outside the coverage area is often undetected by the bump sensor.
In addition, other navigational hazards, such as unnavigable floor surfaces, are typically not detected by the foregoing conventional obstacle detection mechanisms. Examples of unnavigable floor surfaces that may go undetected include a snag on a carpet upon which the robot is caught, a carpet that is too thick for the robot to traverse, a bump, a steep approach angle, or an incline that the robot cannot climb, loose terrain such as mud, loose gravel, uneven rocks, and the like.